Actinomycosis of the lung is probably caused by the germs being inhaled along with the inspired air.
Lesions. The lesions are very peculiar in character, and end in completely destroying the tissues invaded.
Once lodged within an organ, the disease shows a tendency to extend in all directions, and, despite the defensive reaction of the tissues, it soon forms numerous parasitic centres.
In bones, for example, actinomycosis invades the spongy tissue with the greatest ease. It causes subacute ostitis, which leads to diffuse suppuration and local hypertrophy of the bone, destruction of the compact layers, and the development of an abscess with fungoid, exuberant, granulating walls which show no reparative tendency whatever.
The pus of the abscess and the liquid from the fistula contain varying quantities of yellowish grains, representing clusters of actinomyces. The surrounding tissues, muscles, tendons, skin, etc., are all involved before long in the inflammatory process, and the granulating masses themselves are invaded by the yellowish parasitic tufts. All the fistulæ are surrounded by enormous zones of infiltration, which on incision exhibit a lardaceous appearance. On section it may appear that the lesion is confined entirely to the bone, though this is exceptional (Fig. 274). Ordinarily the neighbouring tissues are also destroyed, and not infrequently there is communication with the external air. Sections then display a fungoid tissue, interspersed with perforated lamellæ of bone and lardaceous tissue containing cavities crammed with actinomyces.
Fig. 275.—Highly-magnified clump of actinomyces.
The lesions in the parotid regions, the neck or other parts attacked always present the same appearance, viz., wide, tortuous, bifurcated fistulæ, with exuberant granulations both in the direction of the cavities and of the exterior, together with lardaceous induration of the tissues and abundant fœtid liquid pus.
When it affects the tongue the parasite is to be found in the submucous region, where it causes little swellings, which, when superficial, rapidly undergo ulceration. The subjacent regions, the interstitial connective tissue, and the muscular tissue become infiltrated, hardened and progressively sclerosed. The tongue is gradually hypertrophied, and soon it becomes as hard as wood, whence the term “wooden tongue.”
Actinomycosis of the lung may easily be mistaken for tuberculosis, for the centres, although usually confined to one lobe, may also be disseminated. The lesions, however, are surrounded by an abundant fibro-sclerous inflammatory tissue.